This invention relates to electromagnetic projectile launchers and more particularly to switches for use in switching the very large DC currents employed in the electromagnetic propulsion of projectiles.
Electromagnetic projectile launchers are known which comprise a source of high current, a pair of conductive projectile launching rails, a sliding conductive armature for conducting current between the rails and for propelling a projectile along the rails, and a switch for commutating current from the high current source into the rails and the armature. The electromagnetic forces generated by the injection into the launcher rails of a very large DC current drive the projectile down the rails and out of the muzzle at very high velocities. Various switch designs have been utilized or proposed to perform the rapid switching of high current required in the electromagnetic launching of projectiles.
A rail switch has been used which is actually a second parallel rail device with one of its rails connected to the breech end of each of the launcher rails with a non-conducting section in between. An armature, which is in sliding electrical contact with the rails, is driven down the switch rails by the electromagnetic forces generated by a very large DC current to be switched. When the armature passes the non-conducting section of one switch rail, a massive arc is struck between the armature and a section of one rail which it is leaving. As the armature continues down the switch rails, the arc lengthens, thereby increasing arc voltage which results in the injection of current into the launcher rails. While the rail switch provides rapid commutation of the current into the launcher rails, due to the high speed of the switch armature at the time the arc is struck, it is bulky, expensive and requires means for stopping the armature after commutation, for returning it to the starting point, and for restraining it against the forces generated by the applied current preparatory to a second firing. Thus the rail switch is not adequately suitable for a burst or rapid firing of the launcher.
A rotary switch has been proposed in which a conducting element within a cylindrical rotor is rotated to alternately make and break contact with at least two brush members which are located adjacent the rotor surface. When the rotor is turned to a first position, a very large DC current applied to one of the brush members flows from that brush member through the conducting element on the rotor and out through the other brush member. When the rotor is rotated to a second position, the conducting element is no longer in electrical contact with the brush member to which the very large current is applied, thereby interrupting the flow of this current from the one brush member to the other through the conducting element. This interruption of current flow can be used to inject current into the rails of an electromagnetic launcher. The present invention involves an improvement in the rotary switch concept for use in an electromagnetic projectile launcher which is required to launch a burst of projectiles in rapid succession.
The high current source of an electromagnetic projectile launcher may, for example, include the series connection of a direct current generator such as a homopolar generator, a switch and an inductive energy store. Prior to a launch, the switch would be closed, and the high current source would be shorted by a firing switch, allowing the generator to charge the inductor to a previously determined high current level. Once this current level has been achieved, the firing switch will be opened, thereby commutating current into a pair of projectile launching rails and through a sliding conductive armature between the rails. In order to launch a burst of projectiles in rapid succession and at approximately the same muzzle velocity, the firing switch must alternately close and open, remaining closed between each shot for a time period long enough for the current in the inductive energy store to be increased to the predetermined firing level. If a homopolar generator is used to provide current for the inductive energy store, the generator voltage after each shot will be reduced, thereby requiring a longer charging time to achieve the firing current level in the inductor. Therefore, in order to launch a burst of projectiles at approximately the same muzzle velocity, the firing time of the projectiles will be constant, while the charging time between shots is variable. A rotary switch which performs the firing switch function must therefore be capable of acting as a short across the breech end of a pair of projectile launching rails for a variable time while being in the open circuit position for a fixed time for each shot of a burst. A switch constructed in accordance with the present invention utilizes variable width brush members to meet this requirement.
The present invention switch comprises: a cylindrical rotor; a conducting element extending traversely through and axially along the rotor; a stator having an inner cylindrical surface; two brush members at angularly spaced locations on the stator cylindrical surface, each brush member terminating in an arcuate surface complementary to and in sliding electrical contact with the cylindrical surface of the rotor, with the width of said arcuate surfaces increasing in an axial direction along the stator cylindrical surface; means for rotating the rotor; and means for moving the rotor axially along the stator. An electromagnetic projectile launcher constructed in accordance with the present invention utilizes the above switch and further includes: a source of high current connected between the brush members; a pair of conductive projectile launching rails, each of the rails connected to one of the brush members; and means for conducting current between the rails and for propelling a projectile along the rails. During the launch of a burst of projectiles, the rotor rotates within the cylinder of the stator and travels axially along the stator. Since the brush member width varies axially along the stator, the width of the spaces between the brush members varies inversely in the same direction. Therefore, in order to achieve a variable charging time and a constant firing time during the burst sequence, the rotor must change speed monotonically as it travels along the stator.